Loaders, which include a class of machinery referred to as tractor loader-backhoes or TLBs, are often used in conjunction with dump trucks. In a typical loader arrangement, as shown in FIG. 1, the loader is usually directed into a pile of material to load a bucket of the loader with the material, with the position of the loader depicted as position 1 or P1. After the bucket is loaded with the material, the loader is then placed in reverse gear to back away from the pile toward a position 2 or P2. While executing the backing maneuver from P1 to P2, the operator manipulates the steering device of the wheel loader toward one extreme turning position, also referred to as a lock or lock position, in order to be “lined up” with the dump truck. Typically, the steering device is a steering wheel, and manipulation of the steering wheel is achieved by rotating the steering wheel. However, in order for the operator to be able to move the loader from P2 to P3, the operator must then rotate the steering wheel from the lock position to a center position. Once the loader empties the contents of the bucket into the dump truck at P3, the operator places the loader in reverse gear to move from P3 toward P4. While executing the backing maneuver from P3 to P4, the operator rotates the steering wheel toward a lock or lock position, in order for the loader to be “lined up” with the pile of material. Upon reaching P4, the operator must once again rotate the steering wheel from the lock position to a position before the loader can be directed toward P1 to repeat the process.
Loaders are typically configured to require the operator to rotate the steering wheel six revolutions to steer the loader from one extreme turning position to the other extreme turning position, often referred to as a “lock to lock” maneuver. In other words, for one loading sequence, i.e., moving the loader from P1 to P4, the loader operator must rotate the steering wheel a total of 12 revolutions. Since loader operators must perform the loading sequence many times in a work shift, such extreme repetitive steering movements become physically exhausting for the operator.
Although known steering assist constructions can reduce the number of steering wheel rotations required to achieve an amount of steering change, such as a “lock to lock” movement, such constructions can become awkward, as the operator looses “feel” of the steering.
One steering assist construction, U.S. Pat. No. 6,318,078, is shown diagrammatically in FIGS. 2 and 3. FIG. 2 is directed to metered flow system, while FIG. 3 is directed to a non-metered flow system. As shown in FIG. 2, fluid flows from a source 30 through a line 26, a valve 12, a line 34 and to a gerotor 14, which meters pressurized fluid back through a line 36, valve 12 and then through a line 38 to a steering cylinder 18.
In the non-metered system of FIG. 3 of U.S. Pat. No. 6,318,078, a solenoid valve 20 is activated so that pressurized fluid from source 30 flows through valve 20 through line 34 to actuate a valve 22 so that gerotor 14 is isolated from the rest of the system. That is, pressurized fluid from source 30 flows through line 26, valve 12, line 34 then to line 36 by valve 22, back through valve 12 and then through line 38 to steering cylinder 18. The steering system shown in FIG. 3 acts like a valve instead of a metering unit. That is, in response to a slight actuation or turn of the steering wheel, non-metered pressurized fluid is provided to steering cylinder 18, causing the piston in the steering cylinder to actuate and continue to actuate until the piston reaches the end of its travel or the steering wheel is centered.
In this type of steering, the user controls only the direction of piston movement within the steering cylinder 18, instead of the amount of travel of the piston within the steering cylinder movement as in metered steering. Stated another way, slightly turning and retaining the steering wheel in one direction from the centered position, the wheels are steered toward a corresponding maximum left hand or right hand turn. If system pressure at source 30 is lost for the system of FIG. 3, valve 22 returns to a first position (see FIG. 2) due to the spring in the valve overcoming the fluid force in line 34, and gerotor 14 is again in fluid communication with the system to provide metered flow to the steering cylinder 18. In other words, in such a circumstance, also referred to as an emergency steering mode, the construction of U.S. Pat. No. 6,318,078 shifts from operating as shown in FIG. 3 to operating as shown in FIG. 2.
In summary, while the steering construction of U.S. Pat. No. 6,318,078 may provide non-metered steering assist (FIG. 3), the operator cannot typically control the amount of directional steering change provided, since the operator cannot view the final angular position of the wheels or track of the loader. In other words, this construction does not provide a controlled steering assist construction.
Shown diagrammatically in FIGS. 7 and 8 is a dual displacement steering system produced by Eaton Corporation that includes a pilot line 40 between a source of pressurized fluid source 30 and a valve 22 that provides metered fluid from gerotors 14, 16 to steering cylinder 18 via line 32. In this steering system arrangement, so long as fluid is provided by pressurized fluid source 30, fluid is metered by both gerotors 14, 16, resulting in fewer turns of a steering wheel to achieve “lock to lock” movement. However, this steering system arrangement does not permit the operator to reduce the responsiveness of the steering system by selectively isolating one of gerotor 14 or gerotor 16 from the system. In the case pressurized fluid source 30 becomes non-operational during operation of the loader, constituting an emergency situation outside the control of the operator, as shown in FIG. 8, gerotor 16 is isolated from the steering system, leaving only gerotor 14 to provide metered flow of fluid to streering cylinder 18 to provide steering for the loader. It should be noted in this operation, the displacement of the dual gerotor is sized for normal operation, including high-speed operations or “roading”, while the single gerotor is sized for emergency manual steering.
As background, a “hand pump” serves as the steering device for hydraulic steering machines, which is common for construction equipment and agricultural equipment. This is different than the automotive sector, in that the automotive sector vehicles have a direct mechanical link between the steering wheel and the steering axle; whereas hydraulic steering simply has a hydraulic connection.
The steering wheel is attached to a shaft in the hand pump, which connects to a hydraulic valve and a gerotor. The gerotor and the steering wheel are typically linked to provide a “one-to-one” relationship in rotation. That is, one turn of the steering wheel correlates to one turn of the gerotor. Typically, there is a spring arrangement inside the hand pump, which allows a slight movement (approximately 15 degree steering wheel rotation) before the system requires manual force to effect steering, and it is then a direct “one-to-one” link. Under normal power operations, the steering wheel will lead the gerotor a few degrees, until the power from the hydraulic valve is metered through the gerotor, and to the cylinder. Even with the spring arrangement, the system remains a “one to one” relationship between the steering wheel and gerotor.
When hydraulic power is lost, then the steering system is controlled by manual power. This is why the steering valve is sometimes referred to as the “hand pump”. When the power pump supply is lost, oil is available in the hand pump through an anti-cavitation check valve in the inlet, so the hand pump can generate the pressure. For example, if there was a void in the system, it would be impossible to generate hydraulic pressure in the steering system. Not surprisingly, the larger the gerotor, the greater the turning force that must be applied to the steering wheel to generate a given pressure required by the steering cylinder in order to steer the vehicle. The industry has a guideline on a maximum steering wheel turning force that is acceptable for providing vehicle emergency steering, which is required while a vehicle is driven through a given course.
The existing Eaton dual gerotor is configured for use during emergency steering. As vehicle weights increase, the fluid pressure required to steer them increases, and thus, the force required to effect manual steering likewise increases. However, as noted above, the Eaton construction does not provide selectable multiple ratio steering.
Therefore, what is needed is a steering assist construction selectably controllable by an operator that can reduce the number of steering wheel revolutions required to achieve a predetermined amount of directional change, such as a “lock to lock”, in a dump truck loading configuration, but maintain the higher number of “lock to lock” controlled steering wheel rotations when the loader is not used in a dump truck loading configuration.